“Physical intrusion is now unnecessary to many forms of surveillance,” Justice Sotomayor wrote. In the case of G.P.S. devices, she wrote, “I would ask whether people reasonably expect that their movements will be recorded and aggregated in a manner that enables the government to ascertain, more or less at will, their political and religious beliefs, sexual habits, and so on.”
She went on to suggest that “it may be necessary to reconsider the premise that an individual has no reasonable expectation of privacy in information voluntarily disclosed to third parties.”
“People disclose the phone numbers that they dial or text to their cellular providers; the URLs that they visit and the e-mail addresses with which they correspond to their Internet service providers; and the books, groceries, and medications they purchase to online retailers,” she wrote. “I for one doubt that people would accept without complaint the warrantless disclosure to the government of a list of every Web site they had visited in the last week, or month, or year.”
I'm uncertain what today's ruling by the Supreme Court, saying that the police violated the Constitution when they placed a Global Positioning System tracking device on a suspect’s car and monitored its movements for 28 days, means to companies like Facebook, Foursquare, Apple and Google for instance, but it might make the discussion around online privacy and mobile tracking more interesting.